Sandwich heating machine



June 17, 1958 '.1. R. WHITE ET A1. 2,839,650

SANDWICH HEATING MACHINE Filed Feb.- 14, 195e 4 sheets-sheet 1 June 17, 1958 J. R. WHITE ET AL 2,839,650

SANDWICH HEATING MACHINE Filed Feb. 14, 1956 4 Sheets-Sheet 2 June 17, 1958 J. R. WHITE ET AL SANDWICH HEATING MACHINE;

4 Sheets-Sheet 5 Filed Feb. 14, 1956 NNN June 17, 1958 J. R. WHITE EVAL SANDWICH HEATING MACHINE 4 Sheets-Sheet 4 Filed Feb. 14, 1956 United States Patent O SANDWICH HEATIN G MACHINE Jerome R. White and Kurt R. rlhuler, Chicago, and Jack C. Webb2 Winnetka, Ill., assignors to The .lach Webb Corporation, Chicago, lll., a corporation of Illinois Application February 14, 1956, Serial No. d5,394

7 Claims. (Cl. 219-10.67)

The present invention relates to a method of electronically heating food products and, more particularly, it relates to an electronic unit which is adapted to uniformly heat sandwiches and the like in a short period of time. The invention has particular application to the rapid heating of sandwiches in automatic vending machines in which the sandwiches are stored under refrigerated conditions prior to sale.

Vending machines for sandwiches have become quitepopular in various locations since they remove the need for a paid attendant to dispense the sandwiches. The sandwiches, of course, must be maintained under refrigeration in order to preserve them and while certain types of sandwiches are quite palatable when eaten in the cold state, others are not as appetizing unless they are heated before consumption.

It is the principal object of this invention to provide a heating unit which can be installed in a standard sandwich vending machine and which is operable to effect substantially uniform heating of the sandwiches or the like after they are discharged from storage racks in the refrigerated section and before they are discharged from the discharge chute of the vending machine. Other objects of the invention are the provision of an inexpensive heatinU unit and a method for heating articles of food, such as sandwiches, and the provision of a high frequency heating unit which effects substantially uniform heating of the sandwiches.

Other objects and advantages of the invention will become known by reference to the following description and accompanying drawings of one preferred embodirnent thereof.

In the drawings:

Figure 1 is a top view of a sandwich heating unit embodying various of the features of the invention;

Figure 2 is a sectional view taken along lines 2 2 in Figure l;

Figure 3 is a sectional View taken along lines 3 3 in Figure l;

Figure 4 is a sectional view taken along lines 4 4 in Figure 2 showing a sandwich held in the heating section of the machine; and

Figure 5 is a circuit diagram showing the electronic control and high frequency heating circuit which eect the heating of the sandwiches or the like.

The sandwich heater illustrated in the drawings which, as has been pointed out, is adapted for installation in a vending machine, includes a supporting cabinet 21 and an electronic heating unit 23. The heating unit 23 includes several component sections, i. e., a control section 25, a power supply 27, a high frequency generator e circuit 29, a pair of cooking coils 31 and 31u, and a guiding and holding mechanism 33 (Figs. 1 4) for the articles being heated. The cooking coils 31 and 31a form an integral part of the high frequency generator 29.

The heating unit 23 is enclosed in the cabinet 21 which is desirably of metal to aid in shielding the circuit cornponents. The cabinet 21 is adapted to be placed withrice in an associated vending machine (not shown) and includes an opening 35 on the top thereof (Fig. 2) for receiving sandwiches or other food items to be heated and an opening 37 (Fig. 2l in the bottom thereof for delivering the sandwiches from the heating unit. The cabinet 21 and the openings 35 and 37 are so arranged and proportioned that the cabinet 21 can replace a section of the chute on a standard cold sandwich vending machine so as to interrupt the passage of the sandwich and effect its heating.

For the purpose of clarity, the exact construction of the cabinet 21 and the control section 25 of the electronic system will be described later so that the interrelationships with the other elements of the apparatus will be more readily understood.

Referring now to the circuit diagram, the power supply 27 and the high frequency generator circuit 29 may be of any of several designs will produce electric and magnetic time varying iields of sufficient frequency and intensity from a refrigerated temperature of about 40 F. to a temperature of about 140 F. in about 20 seconds. However, excellent results have been obtained with the circuit which is illustrated in the circuit diagram (Fig. 5) and which has been employed in a commercial ernbodiment 'of the invention.

The illustrated circuit, at the appropriate time in the operation, is connected by the control section 25, as will hereinafter be described, to a source of 105 to 125 volt, cycle, alternating current. rThe power is conducted to the electronic circuit through leads 39, 41 and 41a, lead 39 being connected to one side of the power source and the leads 41 and 41a being connected to the other. Leads 39 and 411 are connected to the input terminals of a plate transformer 43 which, in the commercial embodiment being described, has an output of 1/2 ampere at 3300 volts. The output terminals of the plate transformer 43 are connected to a bank of four diode rectifier tubes 45o, dSb, diie, and 45d in the conventional manner by the leads 47 and 49 and the unnuinbered associated leads, as illustrated, to provide a negative potential of 3300 volts and the necessary current for the high frequency oscillator circuit 29. in the commercial ernbodiment being described, the rectifier tubes are of the 866A type.

The leads 39 and 41a provide a 105 to 125 volt input to a filament transformer :if which is adapted to provide filament current for the four rectifier tubes 45a, 45h,

45e, and 45a', the connections being made as illustrated.

The plates of the tubes 45a and 45d are connected through a lead 53 to the center tap of the filament transformer secondary winding 57 which is adapted to provide lalment current for an oscillator tube 59 in the high frequency oscillator circuit 29. (in the commercial embodiment being described, the tube is an 833A type.) The plates 45a and 45d are by-passed to ground by means of a condenser 55 which, in the commercial embodiment, is a .25 nf., 6000 v. capacitor. rIhe end taps of the filament transformer winding 57 for the oscillator tube 59 are connected to the filament `terminals of the triode oscillator tube 59 by a set of leads 61 and 63. ln the circuit being described, the tube 59 is operated as a class C oscillator to provide the required frequency and power output.

The lead 61 is connected to a condenser 65 which is grounded, the other lead 63 being connected through lead 63a to a condenser 67 which is grounded (in the commercial embodiment of the invention hereinbefore referred to, the co-ndensers 65 and 67 are each 500 fief., 5000 v. mica capacitors). The lead 63o is connected to a grid leak resistor 69 (in the commercial embodiment being described a 5000 ohm, 50 watt) which connects to the grid of the oscillator tube 59.

The tank circuit for the oscillator includes the condensers 71, 73, 74, and '75. The condensers 71 and 73 (in the embodiment being described, each condenser is a 20 auf., 30 kv. vacuum capacitor) are connected as illustrated, the condenser 71 being connected between the plate and grid of the tube 59, and the condenser 74 being connected between the grid of the tube 59 and ground. (In this embodiment being described, the condenser '74 is a l auf., 7.5 kv. ceramic capacitor.) The condenser 73 is connected in parallel with the variable condenser 75 in the lea 77 which connects the grid of the tube 59 to one of the terminals of each of the cooking coils 33 and 31a. The cooking coils 31 and 31a coact with the abovementioned condenscrs and are included in the tank circuit. (The condenser 75 in the hereinabove described commercial embodiment is 3-1t3 auf., 14 kv. variable capacitor.) The plate of the tube 59 is connected to the other terminals of the cooking coils 31 and 3io, as illustrated by the lead 79. @ne of the coils 31a is connected approximately midway of its length to ground through a radio frequency choke Sil. l

This circuit has been found to provide a frequency of 33 to 34 megacycles and to have a plate current of from 400 to 540 milliamperes through the lead '77.

The heating coils 31 and 31a are fabricated from 9/16 inch high-electrical-conductivity copper tubing or rod. The use of tubing because of ease of working and lighter weight may be desirable, but the useof a rod provides rigidity to the units. Each of the coils 31 and 31a is arranged-in one plane and is formed by a number of rectangular convolutions of increasing size to produce the rectangular conguratiou as shown in the drawings. The convolutions of the tube are spaced 1/2 iuch apart (center to center) in the commercial embodiment and the over-all outside dimensions of the coils are about 5 inches by about 5 inches. There are turns. The coils 31 and 31a are identically formed and are disposed to provide additional ields. Thus, when the cooking coils are brought into spaced-apart, face to face position they form a cooking unit, and the respective coils 31 and 31a have opposite convolutions (as shown in Fig. 5). The coils are spaced apart by an appropriate distance. p The coil 31 is connected at its center to the lead '79 which connects to the plate of tube 59 as does the outer convolution of the coil 31a. The coils 31 and 31a are to be connected in the circuit in parallel so that the outer convolution of the coil 31 and the center of the coil 31a are connected to the lead 77 as illustrated which is connected through the condenser network to the grid of the tube 59. The coil 31a intermediate its ends and preferably inthe third convolution from the outside as illustrated is connected to ground through the radio frequency choke S1.

The parallel electrical connection of the coils is an important feature of this invention in providing a practical commercial embodiment.

As will become more clear hereinafter, the sandwich to be heated is disposed between the coils 31 and 31a during heating and becomes a component of the tank circuit. That is to say, the electrical characteristics of the sandwich afect the resonating frequency.

As is shown in the drawings, coils 31 and 31a are arranged in face to face relation and are supported in parallel planes outside a pair of porcelain plates S3 which are spaced apart sufficiently to form a guideway for receiving the sandwich or other article to be heated (Fig. 4).

ln the illustrated circuit arrangement, the oscillator tube is in parallel with only a portion of the tank circuit so that only a portion of the voltage developed by the tank circuit appears across the oscillator tube. This provides longer tube life and permits increased power input to the sandwich.

The circuit is controlled by an electric timing switch (not shown) which is located in the vending machine whichis connected to the electronic heating circuit by Ineens of a Jones-type. QI. other. Suitable plus (Fiss- 3 and 5). The electric timing switch is activated by the coin drop or by any suitable mechanism in the vend ing machine.

in operation, the terminal a of the plug 85 conducts one side of the 105 to 125 volt power supply to the unit. The terminal a is normally connected through a resistance 87 (in the commercial embodiment being described approximately 18 oluns and 25 watts) to the lead 41u to The terminal b of the plug 55 conducts the other side of the 117 Volt power supply to the unit. The terminal b is connected to the lead 31 which connects to the other side of the filament transformer 51 and to one side of the plate transformer 43. This arrangement provides a lament voltage to all of the tive tubes in the circuit of somewhat reduced magnitude so that the tubes remain warm and in an operative condition. The reduction in voltage caused by the resistance 87 lengthens the life of the various tubes in the circuit while maintaining them in condition for almost immediate operation.

The iirst operation effected in the heating cycle by the timing switch in the vending machine is to energize a solenoid 89 through a lead 90 connected to the lterminal g in the plug S5 so as to close a normally open switch 91. The switch 91 through leads 92 and 92u bypasses the resistance 87 so as to apply full voltage tothe primary ofthe filament transformer 51 and thence full filament voltage to the tubes in the circuit. The closing of the switch 91 precedes the application of plate voltage to the tubes 45 by about two seconds. After the tube filaments are at the proper operating temperature, a soienoid 93 is energized by the timing switch through a lead @d connected to the terminal c on the plug 85, connecting its terminals to a source of current, the solenoid 93 is thus energized by the terminals c and b on the plug 85. The solenoid 93 closes the normally open Switch 95 which supplies current to the high voltage plate transformer 43 as well as starting a blower 97 which is operable to cool the oscillator tube 59. In addition, switch 95, when closed, by passes resistance 87 thereby maintaining the full lament voltage when switch 91 opens.

After the desired heating cycle is completed, about 1S to 20 seconds, the the solenoid 93 is de-energized by the timing switch in the vending machine and the switch 95 opens de-energizing the high voltage circuit and turning off the blower 97. At that time the timing switch iu the vending machine actuates a solenoid 99 connected across terminals d and b, which solenoid is operable to discharge the sandwich from between the heating coils 31 and 31a. As the sandwich is discharged from the machine it contacts a feeler arm 101 which actuates a micro-switch 163 to reset the timing switch for the next sandwich to be heated.

The entire unit, as has been heretofore pointed out, is enclosed in a metal cabinet 21. Preferably, the metal cabinet and the arrangement of the circuit elements are as illustrated since this arrangement has been found to reduce parasitic oscillations to a minimum and to minimize interference in surrounding areas. The cabinet illustrated is generally L-shaped in plane View as is illustrated in Figure l, and is fabricated from sheet metal panels and reinforcing members in the conventional manner.

One of the arms of the L is adapted to contain the power supply circuit 27, i. e., the high voltage transformer 43, the solenoid 93, and the switch 95 which supplies current to the high voltage transformer, the solenoid and switch 89 and 91, respectively, for applying voltage to the filament transformer and the resistance 87 for reducing Voltage to the filament transformer during periods of non-use. Also, in this section of the L-shaped cabinet, there are disposed the four rectifier tubes 45a, 45b, 45C, and 45d, as well as the capacitor 45 and the iilament transformer 51. This section of the metal cabinet is completley enclosed by the outer walls of the cabinet, openings of course being provided for the passage of air for ventilation of the power supply compartment.

The high frequency circuit 29, including the heating coils 31 and 31a is enclosed in a box-like metal container 105 which is adapted to provide an effective shield for the high frequency circuit. The container which includes a top, bottom, sides and ends is mounted on suitable insulators 107 within the other arm or section of the L-shaped cabinet. As illustrated, the metal container' 10S is spaced from and insulated from the net at all points except where rod 108 provides an electrical connection between the container and cabinet. lt will be seen that the high frequency circuit is enclosed in a double shield, i. e., the shielding container 105 and the cabinet 21.

The oscillator tube 59 is mounted on the end wall of the container 105 which separates the power supply section of the cabinet from the high frequency circuit section and on this Wall there are also attached the resistance 69 and the condensers 65 and 67. Thus, it will be seen that the oscillator tube 59 and its associated grid-leak resistor and condensers 65 and 67 are all located at one end of the high frequency shielded container 165.

In the central portion of the shielded container 105 there are located the condensers 71, 7.3, 74, and 75 which constitute a part of the tank circuit and, finally, at the end of the shielded section opposite the tube 59 the heating coils 31 and 31a, which are also part of the tank circuit, and the radio frequency choke 81 are supported.

The blower 97 for cooling the oscillator tube is mounted outside of the cabinet 21 (Figs. l and 3) and is positioned to discharge a stream of air through suitable openings into the cabinet 21 and into the shielded container 105 within the cabinet 21 so as to maintain the oscillator tube 59 at the proper operating temperature. This air is of course permitted to escape from the cabinet through suitable openings.

As is illustrated, particularly in Figure 2, the coils 31 and 31a are located beneath a flanged guide or chute 1&9 which fits into the opening in the outer cabinet 21. This hanged guide 109 lits through an opening 111 in the inner shielded cabinet and is adapted to position sandwiches or the like so that it falls into the guideway provided by a pair of end plates of porcelain or the like 113 (Fig. 2) and the porcelain side plates 83 which are arranged on the innermost sides of the heating coils 31 and 31a (Fig. 4). The passage of the sandwich is impeded in the guideway provided by the porcelain plates 83 and 113 during the heating cycle by a horizontally disposed stop finger 115 which is fabricated from plastic or other nonconducting, heat resisting material and which is adapted to slide in a horizontal plane through suitable openings in the cabinet 21 and the shielded inner container 105 so as to block the guideway so as to prevent passage of the sandwich out of the heating section. The linger 115 yis movable inwardly and outwardly of the cabinet 21 and is controlled by the solenoid 99, illustrated in Figure l, by means of a bell crank lever 117 actuated by the solenoid 99 and returned to position by a spring 119 when the solenoid 99 is deenergized as has been heretofore described.

Below the heating section of the unit there is provided a continuation of the porcelain-walled guideway formed by the porcelain plates 33 and 113 which discharges onto an outlet chute 121 (Fig. 2) which, in turn, discharges the heated Isandwich S (Fig. 2) from the machine. As is illustrated schematically in Figure 2, the sandwich S trips the micro-switch 163 by contacting an arm 101 so as to reset the timing switch in the vending machine as has been hereinbefore described so as to ready the unit for another heating operation.

In preparing the sandwiches for use in the foregoing heating unit, it has been found desirable to Wrap the sandwich in paper 123 with unsealed seams so as to permit free passage of expanding gases and moisture which might be caused by the rapid heating of the sandwich (Fig. 4). It is also desirable that the Wrapped sandwich be contained in a cardboard box 125 having dimensions which will readily pass between the porcelain plates 83 and 113 (Fig. 4). 'The cardboard Ibox 125 aids in maintaining the sandwich in good condition during its passage through the machine and, in addition, facilitates such passage particularly in the event that the heating causes the formation of steam within the package due to excessive moisture which might tend to balloon out the sides of the package and causes the package to stick in the machine.

in the foregoing there has been described a heating unit for sandwiches or the like, a high frequency circuit suitable for use in such an apparatus, and a control circuit for the unit. All of the elements which have been hereinbefore described co-act to provide a compact inexpensive heating machine which is particularly adapted for installation in a standard vending machine. The uniform heating of the sandwich is greatly facilitated by the square or rectangular outline of the heating coils 31 and 31a, as well as `by the passage of the high frequency current from the innermost convolution to the outermost on one plate and from the outermost convolution to the innermost on the other plate. The entire circuit and arrangement results in trouble-free and eilicient heating and a unit which is inexpensive to construct and requires a minimum of maintenance.

Various features of the invention are expressly set forth in the following claims.

We claim:

l. A high frequency system which is adapted to effect the rapid heating of food products or the like comprising a high frequency generator circuit having a pair of high frequency heating coils which are connected in parallel in said circuit, said coils having ygenerally rectangular convolutions of increasing size which are positioned in a single plane, said coils being arranged in parallel planes which are spaced apart to receive therebetween the article to be heated, said coils defining an area substantially coextensive with said article, and the inner convolution of each of said coils being connected to the outer convolution of the other of said coils.

2. A high frequency system which is adapted to effect the rapid heating of food products or the like comprising a high frequency generator circuit having a pair of high frequency heating coils which are connected in parallel in said circuit, said coils having generally rectangular con- Volutions of increasing size which are positioned in a single plane, the convolutions of one of said coils being right handed and the convolutions of the other of said coils being left handed, said coils being arranged in parallel planes which are spaced apart to receive therebetween the article to be heated, said coils dening an area substantially coextensive with said article, and the inner convolution of each of said coils being connected to the outer convolution of the other of said coils.

3. A high frequency system which is adapted to effect the rapid heating of food products or the like comprising a Ihigh frequency generator circuit having a pair of high frequency heating coils which are connected in parallel in said circuit, said coils being fabricated from copper tubing arranged in generally rectangular convolutions of increasing size which are positioned in a single plane, the convolutions of one of said coils being right handed and the convolutions of the other of said coils being left handed, said coils being arranged in parallel planes which are spaced apart to receive therebetween the article to be heated, said coils defining an area substantially coextensive with said article, and the inner convolution of each of said coils being connected to the outer convolution of the other of said coils.

4. A high frequency system which is adapted to effect the rapid heating of food products or the like comprising a high frequency generator including a tank circuit and t an oscillator tube operated as a class C oscillator in parallel with only a portion of the tank circuit, a pair of high frequency heating -coils which are connected in parallel in said circuit, said coils having generally rectangular convolutions of increasing size which are positioned in a single plane, said coils being arranged in parallel planes which are spaced apart to receive therebetween the article to be heated, said coils dening an area substantially coeXtensive with said article, the inner convolution of each of said coils being connected to the outer convolution of the other of said coi' convolution ofjone `of said coils being connected to tne plate of said oscillator tube and the outer convolution of the other of said coils being connected through a condenser network to the grid of said oscillator tube.

5. A high frequency 'system which is ada ed to the rapid heating of food products or the like comp a guideway of insulating material having parallel walls between which the article to be heated is disposed during the heating operation, a high frequency generator circuit, a pair of high frequency heating coils which are connected in parallel in said circuit, said coils having generally rectangular convolutions of increasing size which are positioned in a single plane, said lcoils dening an area substantially coextensive with said article, said coils being arranged in parallel planes outside of the side Walls of said guideway.

6. A high frequency system which is adapted to eect the rapid heating of food products or the like comprising a high frequency generator circuit having a pair of lhigh frequency heating coils which are connected in parallel in said circuit, said coils being fabricated from copper tubing having a diameter of about Qi/16 inch arranged in genassenso o* t erally rectangular convolutions-of increasing size which are positioned in a single plane, the convolutions of one of said coils being right lhandedV and the convolutions of the of said coils being left handed, the spacing between said convolntions being about 3/8 inch,` said coils being stra god in parallel planes which are spaced apart to rcceive therebetween the article toV be heated, said coils de lining an area substantially coeXtensive with said article, and the inner convolution of each of said coils being connected to the outer convolution of the other of said coils.

7. A high frequency system which is adapted to effect the rapid heating `of food products or the like comprising a guideway of insulating material having parallel side walls between which the article to be heated is disposed n g the beating opeartion, a high frequency generator cl cuit, a pair of high frequency heating coils which are connected in parallel in said circuit, said coils having generally rectancular ccnvolutions of increasing size which are positioned in a single plane, said coils dening an area substantially coextensive with said article, said coils being arranged in parallel planes outside of the side wall oi said guideway, the convolutions of the coil on one side of said guideway registering with the convolutions of the coil on the other side of said guideway.

References Cited in the tile of this patent UNITED STATES PATENTS 1,566,560 Northrop Dec. 22, 1925 2,686,864: Wroughton et al Aug. 14, 1954 2,733,659 Williams Feb. 7, 1956 2,751,480 Eisen June 19, 1956 

